Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the mobile stations, and the reverse link (or uplink) refers to the communication link from the mobile stations to the base stations. This communication link may be established via a single-in-single-out, multiple-in-single-out or a multiple-in-multiple-out (MIMO) system.
Synchronous hybrid automatic repeat request (HARQ) operation has been adopted for the uplink shared channel (ULSCH) data transmission in the LTE standard for both frequency division duplexing (FDD) and time division duplexing (TDD). In the synchronous transmission, there is a fixed relationship between the HARQ process identifier (ID) and the system time. The system time in general is uniquely defined within a period as t=radio_frame_number*10+subframe number. Accordingly, the HARQ process ID generally does not need to be signaled to a user equipment (UE) in a downlink control information (DCI) message in format 0, as there exists a common understanding between a UE and a base station (e.g., access points, Node B, Evolved Node B eNodeB, eNB) about which process is used in each subframe.
On the other hand, a system frame number (SFN) generally has a limited number of bits which may be defined in the master information block (MIB). The SFN rolls over after reaching the maximum number of supported radio frames. For evolved universal mobile telecommunication systems terrestrial radio access network (E-UTRAN, according to the 3GPP LTE standard), the SFN may be signaled with 10 bits. In order to avoid disruption in synchronous HARQ operation, a similar relationship between the HARQ process ID and the system time needs to be maintained at all times even if the SFN rolls over.
Therefore, there is a need in the art for techniques to avoid disruption of service in synchronous hybrid automatic repeat request operation at system time rollover.